The invention concerns a machine, having a lateral channel and often termed air-ring blowers, comprising an impeller provided with a central body to which peripheral blades are connected. The impeller is closed in a casing which defines a circumferential annular conduit, arranged on the external circumference of the casing, in which the impeller blades rotate. The annular conduit exhibits an intake mouth, through which a fluid is aspirated and enters the machine, and a delivery mouth through which the fluid is expelled from the machine itself.
These machines can function either as vacuum pumps or as compressors. In the first case the induction mouth is connected to the environment where a depression is to be created and the delivery mouth is generally connected to the external atmosphere; while in the second case the induction mouth is generally connected to the external atmosphere and the delivery mouth is connected to the environment where an overpressure is to be created. In both cases the pressure at the induction mouth is lower than the pressure at the delivery mouth, so there exists a Δp between the zone where the induction mouth is and the zone where the delivery mouth is.
The annular conduit exhibits a first tract, which, following the advancement direction of the blades in the conduit, goes from the induction mouth to the delivery mouth, and a second tract, which goes from the delivery mouth to the induction mouth. The first tract has a transverse passage section having greater dimensions than that of the second tract. More precisely, each blade fits the second tract snugly, i.e. it passes at a very tiny distance from the internal walls of the second tract; preferably this distance is the tiniest possible, compatibly with friction problems, so as to prevent fluid passage between the two mouths through the second tract. Between the internal walls of the first tract and the blades a much larger free space is left, wherein turbulent fluid movement can take place.
During operation, the dynamic action of the blades generates a fluid current in the first tract of the annular conduit from aspiration to delivery. The conformation of the annular conduit, and in particular the presence of the free space between the blades and the internal walls of the first tract of the annular conduit is necessary in order for the motion of the blades to effectively give rise to a current of fluid from induction to expulsion.
The impeller is keyed on a shaft, which is usually set in rotation by an electric motor and rotates internally of the casing. At the lower part of the channel the blades of the impeller rotate in, an annular slit is afforded which enables passage of the body of the impeller internally of the casing. Between the internal part of the annular slit and the body of the impeller as small a space as possible must be left, compatibly with the problem of friction, in order to prevent passage of fluid from the channel to the internal part of the casing where the impeller shaft is located. In other words, as far as possible, fluid passage between the delivery and intake mouths, that is, between the zone where the delivery mouth is and the zone where the intake mouth is, should be prevented outside of the lateral channel and in an opposite direction to the direction of the motion of the blades.
However careful the mechanical construction may be, however, it is still inevitable that owing to the difference in pressure between the machine delivery mouth zone and the machine intake mouth zone there is a slight fluid leakage between casing and impeller body, in the opposite direction to the direction determined by the blade action, between the two zones. There is, effectively, always a small amount of fluid which is circulated and re-circulated. This causes the machine temperature to rise, especially in the casing which, if not properly cooled from outside, can reach 90-95° C. and beyond, in the largest machines, temperatures at which it is necessary to shut the machine down.
To limit this drawback the machines have to be installed in airy places so that an excessive temperature rise is prevented. Sometimes, however, in the warm seasons, the machine still has to be shut down during long periods of operation.
The main aim of the present invention is to provide a machine of the type described in which the danger of excessive heating is prevented or at least reduced to a minimum.
A further aim of the present invention is to realise a machine in which there are no significant differences in performance with respect to existing machines.
An advantage of the invention is that it attains the above aims in a constructionally simple and economic way.
A further advantage is that the invention can easily be applied to machines of known type.